Abstract From Middle Jurassic to early Tertiary time, the Western Canada foreland basin filled with mud and silt, and smaller quantities of sand and gravel, derived primarily from the rising cordillera to the west. Most sandstones in the basin are lithic arenites and consist of recycled sedimentary debris, but quartzose and volcano-feldspathicrich sandstones also are abundant. This paper reviews the lithology, diagenesis, and hydrologic history of sandstones in the basin and is based primarily on published studies, government reports, and unpublished university theses. Because hydrocarbon exploration and associated petrologic and hydrologic studies utilizing subsurface drill core and water analyses have focused upon the Alberta portion of the Western Canada foreland basin, this paper also deals primarily with sandstones in the Alberta foreland basin. In spite of the excellent knowledge of the geology and history of this basin, and the abundant, publicly available core, comparatively few diagenetic studies have been carried out. Within the Alberta foreland basin, each eastward-tapering wedge of sandstone is interpreted to reflect a period of extensive tectonism within the cordillera (Bally et al., 1966). Orogenic events in the cordillera are thought to be the result of two major periods of deformation resulting from the collision of foreign crustal fragments with the North American plate during Early to Middle Jurassic time (Columbian orogeny) and mid-Cretaceous to early Tertiary time (Laramide orogeny) (Monger et al., 1982; Stockmal et al., 1992). This paper is divided into three segments. First, the provenance and character of the three major sandstone lithofacies in the

Abstract Thermal recovery projects, in which steam-water mixtures are injected into oil-bearing rocks at high temperatures, provide a laboratory to study rock-water interactions. The temperature range of 80°-220°C is appropriate for diagenetic settings and, because injected steam that condenses to freshwater mixes with more saline water during production, the effect of mixing waters with different salinities can also be examined. In this study of the Tucker Lake pilot site in the Cold Lake heavy oil deposits of Alberta, water and gas samples were obtained at regular intervals over a 7-month period. The chemical composition of these samples was used with solution speciation models to compare the stability of waters with respect to the calculated stability of minerals known to be formed during steam injection and thermal recovery as determined from thermodynamic data. The activity ratios of dissolved species, such as Na + , K+ and Mg 2+ to H + , tend to follow phase boundaries that represent silicate hydrolysis reactions between kaolinite, chlorite, illite, K-feldspar, smectite, and analcime. The Na concentration changes during production from approximately 500 to 4500 mg/L, and the observation that the aNa/aH ratio for the waters follows the smectite-analcime boundary during production suggests that the silicate hydrolysis reaction is buffering the pH to maintain the constant aNa/aH ratio. In contrast, the aCa 2+ /(aH + ) 2 ratio follows the dissolution phase boundary for calcite, implying that the reaction rate for calcite dissolution is more rapid than that for silicate hydrolysis. Other published studies of the isotopic composition of produced gas from the Tucker Lake pilot confirm that CO 2 is produced by reaction of calcite, supporting the role of silicate hydrolysis in calcite dissolution. The buffering of fluid activity ratios by silicate hydrolysis reactions suggests that silicate hydrolysis plays an important role in dissolution of calcite and other carbonates in this thermal pilot, and potentially during natural diagenesis. Silicate hydrolysis and reactions involving silicates in general should be carefully considered in formulating diagenetic models aimed at predicting reservoir quality, particularly if prediction of dissolution porosity is considered an important factor.

Abstract The tar sand and heavy oil deposits of Alberta and Saskatchewan represent a huge resource, most of which has to be recovered by in-situ methods, rather than surface mining. Oil viscosities are extremely high at normal reservoir temperatures and thermal methods of enhanced recovery, primarily steam injection and in-situ combustion, have been successfully employed on a pilot scale. Lithic sands in the Cold Lake area have been subjected to steam injection and pre- and post-steam cores are available for examination of mineral alteration reactions. A core from quartzose sands in the Lloyd-minster area, which was cut after in-situ combustion, is also available and the nature of the mineralogical reactions in these compositionally distinct rocks, subjected to a physically very different recovery scheme, can be compared and contrasted with the Cold Lake samples. Important factors in controlling the extent of mineral alteration include the original composition and mineral distribution of the sands, the temperature and time of exposure to elevated temperature and the water-to-rock ratio. Oil recovery may be affected by mineral reactions if the timing is such that porosity-reducing reactions occur before there has been significant oil displacement. Mineral reactions may also increase porosity and produce CO 2 , both of which are potentially beneficial to ultimate oil recovery.